System for heating liquid by solar radiation

ABSTRACT

A system for heating liquid using solar radiation, includes a plurality of solar panels ( 1, 2, 3, 4, 5 ), at least one reservoir for heated liquid and pipes for circulating liquid between the respective solar panel and the at least one liquid reservoir, the liquid circulating by gravity circulation. The present system is characterised in that a non-return valve ( 17 ) for controlling the flow of heated liquid from the respective solar panel is placed in a portion of the circulation pipe between the upper end of the solar panel and the at least one liquid reservoir, the non-return valve ( 17 ) being adapted to open and close at a predetermined pressure in the liquid flow from the solar panel.

The present invention relates to a system for heating liquid by solar radiation, comprising a plurality of solar panels, at least one reservoir for the heated liquid from the solar panels and pipes for circulating liquid between the respective solar panel and the at least one liquid reservoir. More specifically, the invention relates to such a system wherein the liquid circulates by gravity circulation.

There are already many systems involving the use of one or more solar panels to harness solar radiation for heating a liquid, such as water for domestic use. Two different systems of this type are taught in EP Patent No. 0114005 and U.S. Pat. No. 4,685,445.

According to EP Patent No. 0114005, the reservoir for heated liquid is mounted at a level higher than that of the solar panel and a pump provides circulation of the liquid between the reservoir and the panel. Furthermore, a separate device in the form of a tubular body, located in the flow circuit between the solar collector and the liquid reservoir, is used for correct orientation of the flow of liquid.

The system according to U.S. Pat. No. 4,685,445 differs from the aforementioned solution in that it uses gravity circulation for circulating heated liquid. This means, among other things, that the pump is omitted and the liquid reservoir is mounted level with the solar panel. However, the prerequisite for correct liquid flow is that the flow circuit pipes connecting the solar panel and the liquid reservoir are arranged in a very specific manner.

Furthermore, U.S. Pat. No. 4,782,816 and SE Patent No. 510601 disclose solutions where several solar panels are assembled to form a closed space, e.g., for accommodating circulation pipes and other necessary equipment.

The main object of the present invention is to provide a system that has a compact and efficient structure and that has a shortest possible path for the liquid circulation pipes and fewest possible components connected thereto. This main object is obtained by a system of the type mentioned in the opening paragraph, and which is characterised in that a non-return valve for controlling the flow of heated liquid from the respective solar panel is located in a portion of the circulation pipe between the upper end of the solar panel and the at least one liquid reservoir, the non-return valve being adapted to open and close at a predetermined pressure in the liquid flow from the solar panel.

Since the pressure in the system varies depending upon the temperature reached at any given time during the solar collection, i.e., the pressure increases when the temperature rises and vice versa, it is the pressure difference in the liquid that the float body in the non-return valve responds to in order to open and close the valve respectively.

In this way, correct flow of heated liquid from the respective solar panel is ensured by the non-return valve, which may comprise a valve seat with a central fluid opening, a movable float body for opening and closing the fluid opening and a spindle for controlling the movement of the float body. In a preferred embodiment, the float body is in the form of a thin disc which has an outer element of greater thickness, and the thickness of the outer element can be varied according to the liquid in the system. Furthermore, the at least one liquid reservoir in the system preferably has a large height relative to its dimensions in cross-section.

The circulation pipes for the liquid in the system may be part of a flow circuit which is open to the respective liquid reservoir, and which consists of flow channels in the respective solar panel and a pipe which respectively conveys the liquid from the upper end of the solar panel to the upper end of the liquid reservoir and back from the lower end of the liquid reservoir to the lower end of the solar panel. This allows heated water and make-up water respectively to be taken from and supplied directly to the at least one liquid reservoir. Alternatively, the circulation pipes for the heated liquid may be part of a flow circuit that is closed to the respective liquid reservoir, and which consists of flow channels in the respective solar panel and pipe sections which respectively convey the liquid from the upper end of the solar panel, through the respective liquid reservoir and back to the lower end of the solar panel. In this alternative, the liquid in the system may advantageously be anti-freeze solution, oil, alcohol etc. instead of water.

In the present system at least two solar panels can be joined to each other along their adjacent lateral edges, whilst their outer, free edges are positioned in such relationship to each other that a space is formed between the solar panels for accommodating the at least one liquid reservoir and the circulation pipes. The upper end of the solar panels that constitute the side walls of the formed space may slant downwards in the direction of the joined lateral edges and be covered by a solar panel placed on top of the joined solar panels. Furthermore, the collection of sunrays can be increased by mounting a solar panel on the upper end edges of the solar panels that form the space for accommodating the reservoir and circulation pipes, and/or two additional solar panels which each extend outwards from and are connected to the free lateral edge of the respective joined solar panels. Making the upper end of the solar panels that constitute the side walls of the formed space slant downwards in the direction of the joined lateral edges will enable more of the sunlight to pass over the central solar panels and fall onto the additional solar panels.

The efficiency of the system can be further increased by placing at least one sunlight reflector directly on and/or at a distance from the solar panel or panels in question.

The use of a non-return valve in at least the upper portion of the circulation circuit close to the respective solar panel thus ensures that only solar panels with the desired liquid temperature deliver to the liquid reservoir and prevents solar panels with too low a temperature from “stealing” energy from the active solar panel in the system. The circulation and compactness of the system is further enhanced by the use of at least one liquid reservoir that has a large height relative to its dimensions in cross-section, and which is located in close proximity to the solar panels, and also by the special arrangement of the solar panels.

In addition, as particular advantages of the present invention, brief mention should be made of the fact that the atmospheric pressure inside the at least one reservoir provides rapid circulation and also stable operation during the storage of the heated liquid. The liquid delivered always has a high temperature, even when the system is not fully charged, and the system is scalable through adaptation to the size and shape of and/or the number of solar panels. Moreover, the system is inexpensive to manufacture as it has few components and the path of the liquid flow circuit is short.

The invention will now be described in more detail with reference to the preferred embodiments shown in the attached drawings, in which:

FIG. 1 is a schematic lateral elevational view of a system including a plurality of solar panels according to the invention;

FIG. 2 is a schematic upper end view of the system shown in FIG. 1;

FIG. 3 is a schematic illustration of a second embodiment of the present system supplemented with a sunlight reflector mounted directly on the solar panel;

FIG. 4 is a schematic detailed sectional view of an embodiment of a flow circuit for circulating liquid between a reservoir and the solar panels in the system shown in FIG. 1;

FIG. 5 is a schematic detailed sectional view of a second embodiment of the flow circuit;

FIG. 6 is a vertical section of a non-return valve adapted for controlling the liquid flow in the respective flow circuit;

FIG. 7 is a schematic upper end view of the non-return valve shown in FIG. 6;

FIG. 8 shows a second embodiment of the non-return valve;

FIG. 9 is a schematic elevational view of an embodiment where the system according to the invention is integrated into the facade of a house; and

FIG. 10 is a schematic upper end view of the system shown in FIG. 9.

The present system for heating liquid uses conventional solar panels, and the circulation between solar panels and liquid reservoir takes place by means of so-called gravity flow, i.e., without the use of a pump. Although only one reservoir for heated liquid from the solar panels is shown in the drawings, it will be understood that the system can, when required, comprise more than this one reservoir. The system is intended primarily for use in heating water for domestic purposes in, for example, individual dwelling units such as detached houses and holiday cottages, swimming pools etc. Furthermore, the system can be positioned as an independent unit in the surrounding landscape or integrated in a suitable manner into the facade of the house itself. In conditions of little sunlight, a constant temperature can be obtained in the system in different ways, for example, by using electricity. The system may also be equipped with a heat pump on the solar panels in order to obtain a higher temperature in the liquid, e.g., water.

As shown in FIG. 1, a preferred embodiment of the system according to the invention comprises two main solar panels 1, 2 and three additional solar panels 3, 4 and 5. The main solar panels consist of two upright solar panels that are joined together along one of their lateral edges 12, 14. At the same time, their opposite lateral edges 13, 15 are positioned in such relationship to each other that a space is formed for accommodating a liquid reservoir and a flow circuit for the liquid in the system, consisting of separate pipes or pipe sections and flow channels in the respective solar panel, as shown in FIGS. 4 and 5. One of the additional solar panels 3 is placed on top of the upper end edges of the main solar panels 1, 2 whilst the two other solar panels 4, 5 extend outwards from and are each connected to a free lateral edge of the main solar panels 1, 2.

The two upright main solar panels 1, 2 are set at an angle of 90° in this case, but this angle may of course be varied. The use of more upright main solar panels is also possible, for example, three which are so positioned that the foremost panel extends parallel to the additional solar panels 4, 5, and the two other panels extend backwards, either at right angles from or oblique to the foremost upright solar panel. Alternatively, the main solar panels may be curved, with two or more placed together to form a space having a semicircular cross-section for accommodating the liquid reservoir and the circulation pipes.

Making the upper edge of the two upright solar panels 1, 2 slant forwards in the direction of the joined lateral edges 12, 14 will enable more sunlight to fall onto the upright additional solar panels, thus rendering the system more efficient. The output can be further increased by mounting one or more sunlight reflectors in connection with the present system, i.e., by up to 30% per reflector. Each individual reflector 16 may be placed directly on the solar panel in question, as shown in FIG. 3, or at a suitable distance from the panel, for example, it can be placed directly on the ground (not shown). The reflectors may optionally be reversible, so that they can in a suitable manner be adjusted manually or automatically according to the varying height and/or position of the sun. The output of an independent system may be enhanced by mounting upright solar panels on the rear side of the additional solar panels 4, 5 and above the opening in the space for accommodating, inter alia, the liquid reservoir 6.

The reservoir 6 for receiving the liquid that circulates in the present system is of the upright type, having a large height relative to its dimensions in cross-section, and is, as already mentioned, located in the space formed behind the two upright main solar panels 1, 2 which are joined to each other. As shown in FIG. 4, the liquid circulates in a flow circuit that comprises the liquid reservoir 6 itself, and which otherwise consists of flow channels 21 in the respective main upright solar panel 1, 2 and separate pipes 7, 8 which respectively convey the liquid from the upper end of the solar panel to the upper end of the liquid reservoir and back from the lower end of the liquid reservoir to the lower end of the solar panel. The flow circuit for each one of the upright additional solar panels 4, 5 will have a similar structure. Furthermore, the horizontal additional solar panel 3 has a flow circuit consisting of the flow channels 21 therein and separate pipes 23, 24, 25 running to and from the liquid reservoir 6. The different upper pipes 7, 23 and lower pipes 8, 24 may be passed individually into and out of the liquid reservoir 6, or may optionally be connected for common entry and exit.

In the alternative embodiment shown in FIG. 5, the flow circuit is closed to the liquid reservoir 6, and consists of flow channels 21 in the respective upright main solar panel 1, 2 and pipe sections 9, 10, 11 which respectively convey the liquid from the upper end of the solar panel, through the liquid reservoir and back to the lower end of the solar panel. In this embodiment, the flow circuit for the horizontal main solar panel 3 and the two additional solar panels 4, 5 is conveyed in the same closed manner through the liquid reservoir 6. The liquid from the different solar panels can be conveyed though the liquid reservoir 6 by means of one single or several vertical pipe sections 10.

The embodiment of the flow circuit shown in FIG. 4 is particularly favourable for direct drawing of heated water for use from the liquid reservoir 6 and for topping the reservoir up with fresh water. However, this does not prevent the use of a separate heat exchanger that is placed in communication with the liquid in the liquid reservoir, and which transfers heat energy to water outside the reservoir. The flow circuit shown in FIG. 5 is particularly suitable in those cases where heated water is not to be drawn directly from the liquid reservoir 6, but heat energy is transferred onward by a heat exchanger 22 or the like that is arranged in a suitable manner therein. In such cases, a liquid other than water can be used in the system, e.g., anti-freeze solution or oil.

Correct control of the flow of heated liquid in the flow circuit is ensured by a non-return valve 17 that is located in each individual upper pipe 7, 23 or pipe section 9 between the respective solar panel 1, 2, 3, 4, 5 and the liquid reservoir 6, so that the non-return valve 17 forms the highest point in the flow circuit. The non-return valve 17 is also adapted to open and close at a predetermined pressure in the liquid from the solar panel. This means that the flow circuits will be opened and closed in pulses, so that the hottest solar panel can be tapped for heat energy first. Consequently, the non-return valve 17 in the respective flow circuit will open and close alternately, as the pressure rises and falls to the required level. Each individual non-return valve 17 is equipped with a built-in expansion chamber 29 which has a suitable air valve 30 for releasing any air bubbles which otherwise could bring the system to a halt. The non-return valve 17 may optionally be equipped with a large separate expansion chamber 32, see FIG. 5. According to need, the circulation circuit can in addition be provided with a second non-return valve 31 of a suitable type located in the lower pipes 8, 24, 11, see FIGS. 4 and 5.

The expansion chambers 29, 32 thus deal with any foam formation from the liquid in the circuit. Before operation is started, the circuit is filled to a level where the liquid is above the upper circulation pipe, and then the system is pressurised with air. Optional compression of this air prevents the circuit from bursting. When the reservoir and the circuit are connected, double pressure valves (not shown) may also be mounted so that the system can be closed at a predetermined pressure level. After such closing, the system must be reactivated and pressurised.

As shown in FIGS. 6 and 7, one embodiment of the non-return valve 17 comprises in addition to the parts already mentioned above, a valve seat 18 having a central fluid opening, a movable float body 19 for opening and closing the fluid opening and a spindle 20 for controlling the movement of the float body. As shown in FIG. 7, the spindle 20 is fastened to the valve housing by, for example, three bars. The float body 19 has an inverted conical shape. This means that the non-return valve 17 is prevented from opening when the heated liquid comes from the “wrong” direction. To effect opening and closing of the non-return valve 17, the float body 19 is designed to respond to a predetermined pressure difference in the circuit. To be more precise, the float body must be balanced in such manner that it is lifted up from and lowered down towards the valve seat 18 in response to the pressure difference that occurs when the temperature in the liquid is changed in relation to a given value. This means that the float body 19 must be dimensioned in relation to the change in the liquid's density during the actual temperature change either upwards or downwards. As shown schematically in FIG. 5, each individual circuit may also be equipped with a lower one-way valve of the same type as the upper one-way valve 17, with the exception of the expansion chambers and the air valve. This means that less stringent requirements can be made with respect to the precise dimensioning of the float body 19, as two different pressure zones are established in the system. Suitable materials for the valve housing are brass, steel, acrylic, composite material etc., for the float valve, silicone, acrylic, nylon, composite material etc. and for the seat and the controlling spindle, brass, steel etc.

As shown in FIG. 8, a second embodiment of the non-return valve comprises a two-part valve housing 38, 39 made preferably of a transparent material so that any bubbling and the functioning of the valve in general can be monitored visually. The housing parts 38, 39 are connected to each other in a suitable manner using a seal 40 in the form of, e.g., an O-ring. The valve seat 37 is formed in the upper housing part 39. The spindle 35 for the float body is made of steel, polished or coated, and can be inserted into bores in the housing parts when the valve is put together. Furthermore, the float body has a central, relatively thin portion 33 and an outer portion 34 of greater thickness, and a sleeve-shaped guide 36. The thickness of the outer portion 34 can be varied, so that the weight of the float body can be balanced in relation to the liquid, e.g., water, glycol solution, alcohol and oil, that is used in the system. The underside of the float body can be equipped with a pattern (not shown). Thus, the float body rotates during its movement up and down along the spindle in order to keep this clean. Unlike the valve mentioned above, the inlet and outlet 27, 28 are oriented in a vertical direction. Nor is there an expansion chamber in the valve itself, which means that such a chamber must be mounted separately, e.g., in connection to the outlet.

As shown schematically in FIGS. 9 and 10, the present solar collection system can preferably be integrated into the facade of a house or other building such as a holiday home etc. In the illustrated embodiment, the system consists of just the two main solar panels 1, 2 that are arranged in a house corner, and which are flush with the outside of the house facade. However, it will be appreciated that, for example, the solar collection system shown in FIG. 1 could just as easily be used, with the two additional upright solar panels 4, 5 positioned at a suitable point on one of the facades of the house and flush with its outer side. In that case, the two upright main solar panels 1, 2 and the horizontal additional solar panel 3 will extend outwards in relation to the house facade. 

1. A system for heating liquid by solar radiation, comprising a plurality of solar panels (1, 2, 3, 4, 5), at least one reservoir (6) for heated liquid and pipes (7, 8; 9, 10, 11) for circulating liquid between the respective solar panel and the at least one liquid reservoir, the liquid circulating by gravity circulation, characterised in that a non-return valve (17) for controlling the flow of heated liquid from the respective solar panel is located in a portion of the circulation pipe between the upper end of the solar panel and the at least one liquid reservoir, the non-return valve (17) being adapted to open and close at a predetermined pressure in the liquid flow from the solar panel.
 2. A system according to claim 1, characterised in that the non-return valve (17) comprises a valve seat (18; 37) with a central fluid opening, a movable float body (19; 33, 34) for opening and closing the fluid opening and a spindle (20; 35) for controlling the movement of the float body.
 3. A system according to claim 2, characterised in that the float body is in the form of a thin disc (33) that has an outer element (34) of greater thickness, the thickness of the element being variable.
 4. A system according to claim 1, characterised in that the at least one liquid reservoir (6) has a large height relative to its dimensions in cross-section.
 5. A system according to claim 1, characterised in that the circulation pipes for the liquid form part of a flow circuit that is open to the respective liquid reservoir, and which consists of flow channels (21) in the respective solar panel and pipes (7, 8) which respectively convey the liquid from the upper end of the solar panel to the upper end of the liquid reservoir and back from the lower end of the liquid reservoir to the lower end of the solar panel.
 6. A system according to claim 1, characterised in that the circulation pipes for the liquid form part of a flow circuit that is closed to the respective liquid reservoir, and which consists of flow channels (21) in the respective solar panel and pipe sections (9, 10, 11) which respectively convey the liquid from the upper end of the solar panel, through the respective liquid reservoir and back to the lower end of the solar panel.
 7. A system according to claim 1, characterised in that at least two solar panels (1, 2) are joined together along their adjacent lateral edges (12, 14) and their outer, free lateral edges (13, 15) are positioned in such relationship to each other that a space can be formed between the solar panels for accommodating the at least one liquid reservoir and the circulation pipes.
 8. A system according to claim 7, characterised in that the upper end of the solar panels (1, 2) that form the side walls of the formed space slant downwards in the direction of the joined lateral edges (12, 14) and are covered by a solar panel (3) placed on top of the joined solar panels.
 9. A system according to claim 1, characterised in that a solar panel (4, 5) extends out from and is joined to the free lateral edge (13, 15) of the respective joined solar panels (1, 2).
 10. A system according to claim 1, characterised in that at least one sunlight reflector (16) is placed directly on and/or at a distance from the solar panel or panels in question. 